Porphyrin-containing silicones having increased thermal stability

Abstract

The silicone compositions, in particular silicone oils and crosslinkable silicone compositions, contain porphyrins as heat stabilizer.

What is claimed is: 
     
       1. A method of increasing thermal stability of a silicone composition subject to thermal or thermal oxidative stress, consisting essentially of adding a porphyrin or mixture of porphyrins of the general formulae where ##STR2## R 2  is an identical or different radical selected from the group consisting of --H, --OH, --OR 3 , --COR 3 , --OCOR 3 , --NO 2 , --CN, --F, --Cl, --Br, --I, --SCN, --OCN, --N═N--OH, --NR 3   2  and --SO 3  A and a monovalent hydrocarbon radical having from 1 to 20 carbon atoms which is optionally substituted by --H, --OH, Or 3 , --COR 3 , --COOR 3 , OCOR 3 , --NO 2 , --CN, --F, --Cl. --Br, --I, --SCN, --OCN, --N═N--OH, --NR 3   2 , --N 3   3  B or SO 3  A, where, in the optionally substituted monovalent hydrocarbon radical, non-adjacent --CH═ units are optionally replaced with --N═ units and --CH 2  -- units are optionally replaced with --O--, --S-- or --NH-- units,   R 3  is selected from the group consisting of --H and a monovalent hydrocarbon radical having from 1 to 20 carbon atoms,   A is selected from the group consisting of --H, Na, and K,   B is selected from the group consisting of Cl, F, Br and I,   R 1  is an identical or different R 2  radical or two vicinal radicals R 1  where together with the carbon atoms of the porphyrin ring to which they are bound from a cyclic hydrocarbon radical having from 5 to 10 carbon atoms in which non-adjacent --CH═ units are optionally replaced with --N═ units and --CH 2  -- units are optionally replaced with --O--, --S-- or --NH-- units, where, in the cyclic hydrocarbon radical, --CH═ and --CH 2  -- units are optionally substituted with --H, --OH, OR 3 , --COR 3 , --COOR 3 , OCOR 3 , --NO 2 , --CN, --F, --Cl, --Br, --I, --SCN, --OCN, --N═N--OH, --NR 3   2 , --NR 3   3  B or SO 3  A,   M is a metal selected from the group consisting of Li, Na, K, Rb and Cs, Be, Mg, Sr, Ba, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Ru, Hf, Os, Cd, Hg, Ag, Au, Pd, Pt, Si, Ge, Sn, In and Ce, where, if the oxidation state of M is higher than two, the free valences are satisfied by radicals R 2  or radicals of organosilicon compounds; to a silicone composition of the general formula     R.sup.4.sub.a SiO.sub.(4-a)/2                              ( 3)     and the following optional components     i. a polyorganosiloxane of the formula   --OSi(R.sup.4.sub.2)R.sup.5 Si(R.sup.4.sub.2)O--           (4)     linked to the silicone composition (3), and     ii. a crosslinking additive, where     R 4  is an identical or different, monovalent hydrocarbon radical having from 1 to 18 carbon atoms which are optionally fluoro-, chloro-, bromo-, or cyano-substituted,   R 5  is an identical or different, divalent hydrocarbon radical having from 1 to 18 carbon atoms which are optionally fluoro-, chloro-, bromo-, or cyano-substituted, or a polyoxy-C 1  -C 4  alkylene radical, and   a is 0, 1, 2 or 3.   
     
     
       2. A method as claimed in claim 1, wherein the silicone composition is a silicone oil. 
     
     
       3. A method as claimed in claim 1, wherein the silicone composition is a crosslinkable silicone rubber composition. 
     
     
       4. A method as claimed in claim 1, wherein the porphyrin is fixed on a finely divided support. 
     
     
       5. A method as claimed in claim 1, wherein the prophyrin is first dissolved in a solvent and then added to the silicone composition. 
     
     
       6. A method as claimed in claim 1, wherein the porphyrin is added directly in finely divided form to the silicone composition. 
     
     
       7. A method as claimed in claim 1, wherein the prophyrin is present in an amount of from 250 ppm to 1500 ppm based on the weight of the silicone composition.